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How do scientists know when their experimental results add up to a discovery?

• sigma;the unit that describes how reliable a result is

• Scientists refer to sigma as the "standard deviation." It is the decisive parameter of the Gaussian curve, a mathematical function that describes the distribution of data from many simple experiments. Citing a certain number of sigma directly translates into a probability. Three sigma, for example, is equivalent to a 99.75 percent chance that a future experiment will yield a compatible result

• Identifying a new particle and determining the significance of its signal is quite different from rolling a pair of dice and calculating the probability of the score. Particle physicists have to study background events, which are created by other particles and leave similar signals.

• Scientists need to know characteristic details of both signal and background events to filter the data and obtain a sharper image. If plenty of "photos" and good filtering techniques exist, physicists can reconstruct the "image" of a new particle.

• Simulations are important in order to judge how much an anticipated signal could differ from the expected background noise.

• To calculate the significance of a discovery, we actually simulate a large ensemble of pseudo experiments. For each pseudo experiment we generate a certain number of events that we would have seen in the detector

• You have to understand exactly how your detector is working to determine the background with particular uncertainties